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CapacitiveCurrentInterruptionwithHighVoltageAirbreakDisconnectors
PROEFSCHRIFT
terverkrijgingvandegraadvandoctoraandeTechnischeUniversiteitEindhoven,opgezagvanderectormagnificus,prof.dr.ir.C.J.vanDuijn,vooreen
commissieaangewezendoorhetCollegevoorPromotiesinhetopenbaarteverdedigenopwoensdag14maart2012om16.00uur
door
YajingChai
geborenteHubei,China
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Ditproefschriftisgoedgekeurddoordepromotor:prof.dr.ir.R.P.P.SmeetsCopromotor:dr.P.A.A.F.WoutersThisprojectwasfundedbytheDutchMinistryofEconomicAffairs,AgricultureandInnovationinanIOPEMVTprogram.AcataloguerecordisavailablefromtheEindhovenUniversityofTechnologyLibrary.ISBN:9789038630977
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ToMiloandRuirui
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Promotor:prof.dr.ir. R.P.P. Smeets, Eindhoven University of
Technology/KEMATesting,Inspections&CertificationCopromotor:dr.P.A.A.F.Wouters,EindhovenUniversityofTechnologyCorecommittee:prof.ir.L.vanderSluis,DelftUniversityofTechnologyprof.dring.V.Hinrichsen,DarmstadtUniversityofTechnologyprof.dr.E.Lomonova,EindhovenUniversityofTechnologyOthermembers:dr.D.F.Peelo,DFPeelo&Associatesprof.ir.W.L.Kling,EindhovenUniversityofTechnologyprof.dr.ir.A.C.P.M.Backx(chairman),EindhovenUniversityofTechnology
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Summaryi
SummaryAs lowcost switching devices in high voltage electrical
power supply
systemdisconnectorsbasicallyhaveaninsulationfunctiononly.Nevertheless,theyhaveavery
limited capability to interrupt current (below one Ampere), e.g.
fromunloaded busbars or short overhead lines. The present study is
a search
forpossibilitiestoincreasethecurrentinterruptioncapabilitywithauxiliarydevicesinteracting
with the switching arc. In this project the state of the art
ofdisconnectorswitchingisinvestigatedandaninventoryispresentedofmodelsofthe
free burning arc in air. A series of experiments were arranged at
differentlaboratories.Theswitchingarcandtheinterruptionprocessarestudiedindetailthrough
electrical andopticalmeasurements during the switchingprocess for
adisconnector with (without) auxiliary devices under high voltage
(0.5
30A,300kV)conditions.Threeoptionsforauxiliarydeviceswereinvestigated:(i)arccoolingbyforcedairflow;(ii)fastinterruptingbyhighvelocityopeningcontacts;(iii)
reduction of arc energy by adding resistive elements. Finally, a
qualitativedescription isprovidedon thephysicalnatureof
thearcandhowtheevaluatedmethodsaffectthearccharacteristics.Allresultsareobtainedbyanalysisofhighresolutionmeasurementofarccurrent(includingallrelevanttransients),voltagesacrossthedisconnectorandhighspeedvideoobservation.Itwas
found that, depending on the current to be interrupted, the
interruptionprocessisgovernedbythedielectricand/orthermalprocesses.In
thedielectric regime, the interrupted current is low
(roughlybelow1A)
andtheswitchingarcischaracterizedbyahighrateofrepetitionofinterruptionsandrestrikesthatonlyceaseafterasufficientgapspacinghasbeenreached.Therestrikesinteractseverelywiththecircuitryinwhichthedisconnectorisembedded,exciting
transients in current and voltagewith frequenciesup to
themegahertzrange.Highovervoltagescanbegenerated.Theirmagnitudescanbelimitedbyaproperchoiceofthecapacitanceatsupplysideofthedisconnector.Thearccircuitinteraction
has been studied and relevant processes have been modelled
andverifiedbyexperimentsinfullpowertestcircuits.In the thermal
regime, the switching arc behaves less vehemently,
interruptingandreignitingbasicallyoccurateverypowerfrequencycurrentzero.Becauseofthepresenceofsufficientthermalenergyintheswitchinggapalongthearcpath,the
voltage to reignite the arc is limited, and the arccircuit
interaction is
lesspronounced.Thoughnotproducingverysevereovervoltages,
thearcdurationislongerandthecurrentmaynotbeinterruptedateverycurrentzerocrossing.Theultimate
thermal regime is reachedwhen thearc continues toexist
afterpowerfrequencycurrentzerowithoutanyappreciablevoltagetoreignite.Thissituation
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iiSummary
mustbeavoidedbecausearcinggoesonuntilahigherlevelbreakerinterruptsthecurrent.
Before this, the arc can reach far away from its roots and can
greatlyreduceinsulationclearance.Themainfactorsinfluencingtheinterruptionperformancearethelevelofcurrenttobeinterrupted,thesystemvoltage,theratioofcapacitancesatbothsidesofthedisconnector
and the gap length.These factors influence the energy supplied
tothe arc upon restrike. This energy extends the arcing time by
lowering
thebreakdownvoltage.Ithasbeenobservedthatthearcinitsthermalmodealwaysreignitesinitsformertrajectory.Keytotheinterruptionprocessisthereductionofbreakdownvoltageinthispath,createdbyhotgasesremainingfromtheformerarc.
The existing breakdown models are reviewed in order to understand
theinfluenceofhightemperatureaironthebreakdownprocess.Basedon
theobservedarcbehaviour,variousmethodshavebeenresearched
toincreasetheinterruptioncapability.The most successful methods are
those that remove the residual (partially)ionizedair from
thearcpath.Experimentswere carriedout todemonstrate
theeffectiveness of air flow directed into the arcs foot point. A
substantial gain ininterruptioncapability isdemonstrated,butat
thecostofgenerating reignitiontransients at a very rapid
succession. Specifically, the experiments showed
that7.5Acouldbeinterruptedsuccessfullyat90kVrmsvoltagewithashorterarcingduration(afactorof0.5wasobserved)thanwithoutairflow.Withapplicationofair
flow, the frequencyof reignitionsoccurring, and
thebreakdownvoltagearemuchhigherthanwithoutairflow.Anothermethod,theassistanceofanauxiliaryswitchabletoproduceaveryfastopening,wasalsosuccessful.Herein,thearcisforcedmechanically
intoambientcoolair,thusavoidingaccumulationofthermalenergyinthearcpath.Specifically,itcaninterruptcurrentsupto7Aat100kVrmssafelyand9Aat90kVrmsintheexperiments
with arcing time only a few tens of milliseconds instead of a
fewseconds. The arc exhibits a "stiff" (linear) character instead
of the
"erratic"(randomlymoving)arcmodewithadisconnectoralone.Thismethodreducesthenumberofrestrikes.The
possible influence of energy absorbing elements (resistors) is
investigatedthrough circuit modelling, supported by some laboratory
experiments. Othermethods, such as the application of series
auxiliary interrupting
elements(vacuum,SF6interrupterandablationassistedapproaches)havebeenevaluated.From
the practical point of view, the auxiliary fastopening interrupter
isrecommendedduetoitseconomic,simpleandeffectivemerits.Otherapproacheshave
certain disadvantages. The method with air flow needs a
complexconstructioninordertointroducethecompressedairflowintothedisconnector,
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Summaryiiiand the hazard for nearby equipments from the
overvoltages caused by theinterruption is greater.Themethodof
inserted resistor requiresveryexpensivearrangement. Regarding the
application of auxiliary interrupters, vacuuminterrupters have to
be applied in considerable numbers in series and SF6interrupters
have good performance but at very high cost. An ablation
assistedapproachseemslesspromisingbecausetheleveloftheinterruptedcurrentistoolowtobeeffective.
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ivSummary
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Samenvattingv
SamenvattingScheidingsschakelaars, of kortweg "scheiders", zijn
relatief eenvoudigeschakelaars inhoogspanningsnettendie
inprincipeenkel een isolerende
functiehebben.Nietteminbezittenzeeenzeerbeperktvermogenstromen(totca.1A)teonderbreken,
zoals bijv. afkomstig van onbelaste railsystemen of
kortehoogspanningslijnen. Deze studie bevat een onderzoek naar
mogelijkheden
hetstroomonderbrekendvermogenvanscheiderstevergrotenmethulpmiddelendiedirect
ingrijpen inde schakelende lichtboog.Om tebeginnen isde
standvandetechniekophetgebiedvanschakelenmetscheidersonderzochtenerwordteenoverzicht
gegeven van het modelleren van vrij brandende lichtbogen in
lucht.Tevensiseenserieexperimentenuitgevoerdindiverselaboratoria.Hierinzijndeschakelende
lichtboog en het onderbrekingsproces in detail bestudeerd
doormiddel van elektrische en optische metingen gedurende het
schakelen onderhoogspanning (0.5 30A, 300kV) met en zonder
hulpmiddelen. Drie mogelijkhulpmiddelen zijn onderzocht: (i)
koeling van de lichtboog door
beblazingmeteengeforceerdeluchtstroom;(ii)onderbrekingmetzeersnellecontactseparatiesnelheid;
(iii) reductie van lichtboog energie door toevoeging van
resistievecomponenten. Tot slot wordt een kwantitatieve
beschrijving gegeven van delichtboog en hoe de boven beschreven
methoden ingrijpen in diversekarakteristiekenvandelichtboog.Alle
resultaten zijn verkregenmet behulp vanmetingenmet hoge resolutie
vanlichtboog stroom en spanning (inclusief hun transinten) alsmede
doorobservatiemetsnellevideotechnieken.Afhankelijk van de grootte
van de te onderbreken stroom, wordt
hetonderbrekingsprocesgekenmerktdoordilektrischeen/ofthermischeprocessen.Inhetdilektrischeregimeisdeteonderbrekenstroomklein(ruwwegbeneden1A)
en de scheider lichtboog wordt gekenmerkt door een zeer
snelleopeenvolgingvanonderbrekingenenherontstekingen.Ditprocesstoptwanneervoldoendecontactafstand
isbereikt.Alsgevolgvandeherontstekingen isereenheftige
wisselwerking met het elektrische circuit waar de scheider deel
vanuitmaakt. Herontstekingen wekken daarbij transinten op in zowel
stroom alsspanning met frequenties tot enkele megahertz. Hoge
overspanningen kunnenhierbij optreden. De hoogte hiervan kanworden
beperkt door een juiste keuzevan capaciteit aan de voedende zijde
van de scheider. Dewisselwerking tussenlichtboog en circuit is
bestudeerd; de relevante processen zijn gemodelleerd
engetoetstmetexperimenteninhoogvermogenbeproevingscircuits.Inhet
thermische regimegedraagtde lichtboog zichminderheftig,
onderbreektde stroom en herontsteekt in principe pas op iedere
nuldoorgang van denetfrequente stroom. Vanwege de aanwezigheid van
voldoende thermische
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viSamenvatting
energieinhetlichtboogpadtussendecontactenisdespanningnodigomdeboogte
herontsteken beperkt en daarmee is de wisselwerking tussen
lichtboog encircuit minder uitgesproken. Hoewel de overspanningen
beperkt zijn, is delichtboogduur langer en wordt de stroom niet bij
iedere
netfrequentenuldoorgangonderbroken.Demeestuitgesprokenthermischeverschijningsvormis
die waarin (bij verdere verhoging van de stroom) de lichtboog bij
elkenuldoorgang herontsteekt zonder meetbare spanning. Deze
situatie dientvermeden teworden omdat de lichtboog in deze situatie
nietmeer dooft en destroom enkel nog door een vermogensschakelaar
onderbroken kan worden.Hieraanvoorafgaandkande
lichtboogveruitwaaierenende isolatieafstand
totandere,onderspanningstaandedeleninhetstation(tezeer)verkleinen.Debelangrijkstefactorendiehetonderbrekingsprocesbenvloedenzijndehoogtevan
de te onderbreken stroom, de netspanning, de verhouding van
capaciteitenter weerszijden van de scheider en de momentane
contactafstand. Dezeparameters bepalen de energie die aan de
lichtboog wordt toegevoerd op
hetmomentvanherontsteking.Dezeenergieverlengtdelichtboogduurdoordatdezededoorslagspanningreduceert.Uitwaarnemingblijktdatinhetthermischregimedelichtboogherontsteektinhetvoormaligelichtboogpad.Hieruitwordtafgeleiddat
de essentie van het onderbrekingsproces de reductie van
doorslagspanninglangs dit pad is. Deze reductie wordt veroorzaakt
door hete gassen en
restionisatieafkomstigvande(vorige)lichtboog.Voorhetbegrijpenvandeprocessendie
leiden tot reductie van doorslagspanning bij temperatuur verhoging
van deluchtzijndebestaandedoorslagmodellenbestudeerd.Op basis van
de boven beschreven waarnemingen van het onderbrekingproceszijn
diverse methoden onderzocht die kunnen leiden tot vergroting van
hetstroomonderbrekendvermogenvanscheiders.Het meest succesvol zijn
methoden die de gedeeltelijke geoniseerde luchtverwijderen uit het
voormalige lichtboog pad. Experimenten zijn
uitgevoerdwaarindeeffectiviteitbestudeerdwordtvanbeblazingvandevoetpuntenvandelichtboogmetkoude
lucht.Eensignificanteverhogingvanstroomonderbrekendvermogen wordt
inderdaad vastgesteld, echter ten koste van de generatie vanzeer
snel opvolgende en hoge herontstekingen die steile
spanningfrontengenereren.Deexperimententonenaandatbijeenfaseaardespanningvan90kVstromen
tot ca. 7.5A succesvol onderbroken worden met een 50%
korterelichtboogduurdanzonderbeblazing.Een andere methode bestaande
uit het gebruik van zeer snel opendehulpcontacten om daarmee in
zeer korte tijd een grote contactafstand terealiseren, blijkt
eveneens succesvol. Op deze wijze worden de lichtboogvoetpunten
zeer snel naar koele lucht getrokken waardoor een te
grotethermischeenergiedichtheidvoorkomenwordt.Opdezemanierkunnenstromenvan
7A (bij 100kV) en 9A (bij 90kV) onderbroken worden, terwijl de
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Samenvattingviilichtboogduur slechts enkele tientallen
milliseconden bedraagt in plaats vanseconden bij toepassing van
conventionele contacten. De uiterlijkeverschijningsvorm van de boog
verandert hierbij van "dansend" (opwaartsbewegendmet
veleuitstulpingen)naar "strak" (rechtlijnig brandend als
kortsteverbinding tussende contacten).Het aantal
herontstekingenblijft
hiermeeookbeperkt.Ookdemogelijkeinvloedvanenergieabsorberendeelementen(weerstanden)isonderzochtmetmodellering,ondersteundmetenigelaboratoriumexperimenten.Alternatieven,
zoals het gebruik van serie geschakelde onderbrekers
(vacum,SF6onderbrekersenonderbrekinggebaseerdopablatie)zijngevalueerduitdeliteratuur.Ter
vergroting van het stroom onderbrekend vermogenwordt vanuit
praktischoogpuntdemethodemetdesnellehulpcontactenaanbevolenvanwegeprestatie,eenvoud
en prijs. Andere methoden hebben duidelijke nadelen. Beblazing
metlucht vereist een ingewikkelde constructie om gecomprimeerde
lucht in
denabijheidvandeschakelendecontactentebrengenenheeftalsbijkomendnadeeldegeneratievansteilespanningsfrontentijdensdeonderbreking.Hetaanbrengenvanweerstandenvereistdureaanpassingen.HulponderbrekersinvacumofSF6gasiseffectiefmaarkostbaarenconstructiefingewikkeldvanwegedehoogtevande
spanning die serie schakeling van elementen vaak nodigmaakt.
Oplossingenmet behulp van ablatie zijn minder kansrijk omdat de
stroom hiervoorwaarschijnlijktelaagis.
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viiiSamenvatting
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Contentsix
Contents
SUMMARY..................................................................................................................................ISAMENVATTING.....................................................................................................................VCONTENTS..............................................................................................................................IXCHAPTER1...............................................................................................................................1HIGHVOLTAGEAIRBREAKDISCONNECTORS.............................................................1
1.1DEFINITIONOFDISCONNECTORS..................................................................................................11.2TYPEOFDISCONNECTORS..............................................................................................................11.3INTERRUPTINGCURRENTWITHDISCONNECTORS......................................................................31.4STANDARDIZATIONSTATUS...........................................................................................................41.5OBJECTIVEOFTHESIS.....................................................................................................................5
CHAPTER2...............................................................................................................................9LITERATUREREVIEW...........................................................................................................9
2.1AWARENESSOFTHECAPACITIVECURRENTINTERRUPTIONWITHDISCONNECTORS...........92.2FUNDAMENTALASPECTSOFCAPACITIVECURRENTINTERRUPTION....................................142.3TRANSIENTSCAUSEDBYCAPACITIVECURRENTINTERRUPTION..........................................162.4APPROACHESTOENHANCETHEINTERRUPTIONCAPABILITY...............................................172.5ARCMODELSRELATEDTOCURRENTINTERRUPTIONWITHADISCONNECTOR..................262.6CONCLUSION.................................................................................................................................29
CHAPTER3............................................................................................................................35BASICCIRCUITANALYSIS.................................................................................................35
3.1THEINTERRUPTIONPROCESS.....................................................................................................353.2THREECOMPONENTSANALYSIS................................................................................................373.3SIMULATIONOFRESTRIKES.......................................................................................................413.4RESTRIKETRANSIENTSINDISTRIBUTEDELEMENTLOADCIRCUITS...................................433.5CONCLUSION.................................................................................................................................45
CHAPTER4............................................................................................................................47EXPERIMENTALSETUP.....................................................................................................47
4.1HIGHVOLTAGESOURCE...............................................................................................................474.2MEASUREMENTSYSTEM..............................................................................................................514.3DISCONNECTORMAINBLADESOPENINGVELOCITY................................................................574.4CONCLUSION.................................................................................................................................59
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xContents
CHAPTER5............................................................................................................................61CURRENTINTERRUPTIONMECHANISM.....................................................................61
5.1EXPERIMENTALOBSERVATIONS................................................................................................615.2ARCINTERRUPTIONCHARACTERISTICS....................................................................................695.3DISCONNECTORCONTACTSSPACING.........................................................................................755.4RESTRIKEVOLTAGE....................................................................................................................765.5ELECTRICALARCCHARACTERISTICS.........................................................................................805.6ENERGYINPUTINTOTHEARC....................................................................................................825.7TRANSIENTSUPONRESTRIKE...................................................................................................855.8CONCLUSION.................................................................................................................................885.9RECOMMENDATIONFORSTANDARDIZATION...........................................................................90
CHAPTER6............................................................................................................................91INTERRUPTIONWITHAIRFLOWASSISTANCE.........................................................91
6.1EXPERIMENTALSETUP................................................................................................................916.2EFFECTOFAIRFLOWONARCING...............................................................................................926.3INTERRUPTIONDATAANALYSIS.................................................................................................976.4CONCLUSION...............................................................................................................................103
CHAPTER7..........................................................................................................................107HIGHVELOCITYOPENINGAUXILIARYINTERRUPTER........................................107
7.1OPERATINGPRINCIPLE..............................................................................................................1077.2EXPERIMENTALSETUP..............................................................................................................1087.3OVERVIEWOFTHEEXPERIMENTALRESULTS........................................................................1097.4RESTRIKEVOLTAGE..................................................................................................................1147.5ENERGYINPUTINTOTHEARC..................................................................................................1177.6CONCLUSIONANDRECOMMENDATION...................................................................................120
CHAPTER8..........................................................................................................................123INTERRUPTIONWITHINSERTEDRESISTORS.........................................................123
8.1SERIESRESISTOR........................................................................................................................1238.2PARALLELRESISTOR..................................................................................................................1288.3DISCUSSION.................................................................................................................................130
CHAPTER9..........................................................................................................................133PREBREAKDOWNPHENOMENAINDISCONNECTORINTERRUPTION...........133
9.1CLASSICALMODELLINGOFBREAKDOWN................................................................................1339.2PREBREAKDOWNCURRENTINDISCONNECTORINTERRUPTION.......................................1379.3DISCUSSION.................................................................................................................................138
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Contentsxi
CHAPTER10........................................................................................................................141CONCLUSIONSANDRECOMMENDATIONSFORFUTURERESEARCH...............141
10.1CONCLUSIONS...........................................................................................................................14110.2PROPOSEDFUTURERESEARCH..............................................................................................146
PUBLICATIONSRELATEDTOTHISWORK................................................................147NOMENCLATURE...............................................................................................................149ACKNOWLEDGEMENT.....................................................................................................153CURRICULUMVITAE........................................................................................................155
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xiiContents
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HighVoltageAirbreakDisconnectors1
Chapter1
HighVoltageAirbreakDisconnectors1.1DefinitionofdisconnectorsHigh
voltage disconnectors are commonly used switching devices in
powersubstations. According to the International Electrotechnical
Vocabulary IEVnumber 4411405 [1], the definition of a disconnector
(DS) is: "A mechanicalswitching device, which provides, in the open
position, an isolating distance inaccordance with specified
requirements". In IEEE standard C37.1001992
[2],insteadoftheterm"disconnector",theterms"disconnecting","disconnectswitch"or
"isolator" are used, defined as "A mechanical switching device used
forchangingtheconnectionsinacircuit,orforisolatingacircuitorequipmentfromthesourceofpower."Bothdefinitionsaresimilar.Theydefinethattheprinciplefunction
ofDSs is to provide electrical and visible isolation from the
system. Inaddition, theymust open and close reliably, carry current
continuouslywithoutoverheating,andremainintheclosedpositionunderfaultcurrentconditions[3].Thedisconnectiongenerallycoverstwoaspects[4]:
Disconnectionrelatedtoordinarydailyoperationofthesystem.
Disconnection related to maintenance of transmission lines or
substation
equipmentsuchastransformers,circuitbreakers,capacitorbanksandsoon.For
power system, personnel safety practices normally require a
visiblebreakasapointofisolation.AnopenDSmeetsthisrequirement.
1.2TypeofdisconnectorsDSs in Gas Insulated Substations are out
of the scope of this thesis. Only highvoltageDSs in the atmospheric
air are studied.TheHVairbreakDS comes inavariety of types and
mounting arrangements. The most common fourconfigurations are:
verticalbreak, centrebreak, doublebreak, and pantographtype. They
can be mounted in various orientations, depending on the
spaceofferedbythesubstation[3],[4].The verticalbreakDS is presented
in Figure1.1 (left). This type ofDS is
highlysuitableinicyenvironmentsthankstoitsrotatingbladesdesign.Itscontactdesignallows
for application in installations where high fault current
situations
mayoccur.TheactivepartsofthistypeDSarethehingeendassembly,theblade,andthe
jaw end assembly. The smaller of the two insulators at the left
rotates andrives theblade to openor close. It is usually
horizontallymounted as shown in
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2Chapter1
Figure1.1. (left)AthreephaseverticalbreakDSmountedhorizontally
inaclosedposition(CourtesyofHAPAMB.V.);(right)centrebreakDSinaclosedposition(CourtesyofSiemens).Figure
1.1 (left). It can also be vertically mounted, i.e. the blade is
verticallyoriented in closed position. The verticalbreak DS
requires minimum
phasespacing.AnexampleofacentrebreakDSisillustratedinFigure1.1(right).ThistypeDSisused
mainly in locations with low overhead clearances. However, it
requireslarger phase spacing than a verticalbreak DS. The active
parts consist of twoblades, disconnecting at the centre. Both
insulators rotate in a vertical plane
toopenorclosetheDS.AdoublebreakDSisavariationofacentrebreaktypeandisshowninFigure1.2(left).
The active parts are two jaw assemblies, one at each end, and a
rotatingblade.ThecentreinsulatorrotatestoopenorclosetheDS.Theycanbeinstalledinminimum
overhead clearance locations and require minimum phase
spacing.Their field of application includes icy environments due to
the rotating bladesdesignandinstallationsinhighfaultcurrent
locationsduetothecontactdesign.This design provides for two gaps
per phase, allowing to interrupt
significantlyhighercurrentthanthesinglebreaktypeDSs[3],[4].Thisisbecausethesystemvoltageisdistributedacrosstwogaps.ThepantographDStype,showninFigure1.2(right),isusedworldwide(butonlyoccasionally
in North America) for Extra High Voltage application,
345800kV.Theactivepartsconsistofafixedcontactsarrangementattachedtothebusbaratthetop,ascissortypebladeandahingeassemblyatthebottom.Thesmalleroneof
the two insulators rotates to open or close the DS. This type DS
normallyprovides transitions from high to low busbars, together
with providing
visibleseparationatthesametime.Thismethodrequirestheleastspace.
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HighVoltageAirbreakDisconnectors3
Figure 1.2. (left)DoublebreakDS in an open position; (right)
pantographDS in a
closedposition(CourtesyofHAPAMB.V).1.3InterruptingcurrentwithdisconnectorsDisconnectors
disconnect unloaded circuits in order to accomplish
visibleisolation. However, they are operated under energized
conditions and willtherefore interruptsomecurrent.Themagnitudeof
thiscurrentdependsonthespecificsituations.AlthoughDSsdonothaveanycurrentinterruptionrating,theydo
have a certain interrupting capability, but it is limited due to
their slowlymovingcontacts.OvertheyearsDSshavebeenappliedto
interrupttransformerexcitation currents, capacitive currents from
short lengths of bus, cable oroverhead line and small load
currents. In this case, very small current
isinterruptedagainstfullsystemrecoveryvoltage(RV).Anothermajorapplicationis
bus transfer switching. In this case, often the full load current
has to
betransferredintoaparallelpath.BecauseofmanydifferentconditionsunderwhichtheDSsmustinterruptcurrents,nointerruptingratingsareassigned[5].Themainapplicationswhereacurrentistobeinterruptedare[4]:
TransformermagnetizingcurrentIt
isalsocalledexcitationcurrent.Thecurrentisusually
lessthan2A,oftenlessthan 1A at 100% excitation voltage, for todays
transformers. The current isgenerally described in terms of an
equivalent RMS value derived from the
corelossmeasurementbythemanufacturer. CapacitivecurrentThis
current, also called charging current, arises from connected short
busbars,short unloaded transmission line, instrument transformers
and other
elementshavingstraycapacitance.Theyactasacapacitiveload.ThetypicalrangeofthesecurrentsforstationairbreakequipmentisshowninTable1.1[6].
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4Chapter1
Table1.1Typicalcapacitivecurrentrangeinoutdoorsubstations(50Hz).
LoopcurrentLoopsarecreatedwhen theDScommutesor transferscurrent
fromonecircuit,suchasabusbaror transmission line, toaparallel
circuit.The loopcurrent canreach up to the full load current in
practice. This current has to be
switchedagainstaverylowvoltage(thevoltageacrosstheparallelpath)[4].1.4StandardizationstatusA
small current interruption capability of the DSs has been
recognized by bothIEEE and IEC standards. In the IEC standard [7],
apart from the definition
andbasicfunctionoftheDS,thecurrentinterruptingcapabilityisaddressedinthreenotes:NOTE1:
Adisconnector is capableofopeningand closinga
circuitwheneithernegligiblecurrentisbrokenormade,orwhennosignificantchangeinthevoltageacrosstheterminalsofeachofthepolesofthedisconnectoroccurs.NOTE
2: "Negligible current" implies currents such as the capacitive
currents of
bushings,busbars,connections,veryshortlengthsofcable,currentsofpermanentlyconnectedgradingimpedancesofcircuitbreakersandcurrentsofvoltagetransformersanddividers.Forratedvoltagesof420kVandbelow,a
currentnot exceeding0.5A isanegligible current for thepurposeof
thisdefinition; forratedvoltageabove420kVandcurrentsexceeding0.5A,
themanufacturershouldbeconsulted.NOTE3:Foradisconnectorhavingaratedvoltageof52kVandabove,aratedabilityofbustransfercurrentswitchingmaybeassigned.SimilarlyintheIEEEstandard[8],thefollowingnoteismade:NOTE:Itisrequiredtocarrynormalloadcurrentcontinuously,andalsoabnormalorshortcircuit
currents for short intervalsas specified. It isalso required to
open or close
circuitseitherwhennegligiblecurrentisbrokenormade,orwhennosignificantchangeinthevoltageacrosstheterminalsofeachoftheswitchpolesoccurs.An
earlier version of the IEEE standard did include the following note
andindicatedthethreetypesofcurrentwithoutexplanation[9].
Equipment Capacitivecurrent(A)72.5kV 145kV 245kV 300kV 420kV
550kVCT 0.04 0.04 0.04 0.05 0.08 0.1CVT(4F) 0.05 0.11 0.18 0.22 0.3
0.4Busbars/m 1.7104 0.32103 0.54103 0.66103 0.84103 1.1103
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HighVoltageAirbreakDisconnectors5
NOTE:Adisconnectingswitchandahorngapswitchhavenointerruptingrating.However,itisrecognizedthattheymayberequiredtointerruptthechargingcurrentofadjacentbuses,supports
and bushings. Under certain conditions, theymay interrupt other
relatively lowcurrents,suchas:
1. Transformermagnetizingcurrent.2. Chargingcurrentsof
linesdependingon length,voltage, insulationandother local
conditions.3. Smallloadcurrents.
Apartfromtheaboverecognition,therearenostandardsorrequiredratingsforthe
current interruption by DSs. Both standards only refer to the
currentcapability of the DS, and both use the word "negligible" to
qualify the
smallcurrent.Bothpointoutthepotentialcurrenttypesandthepossiblesource,whichcausesthesesmallcurrents.ThedifferencebetweenthetwostandardsisthattheIEC
standard defines the meaning of "negligible current" and quantifies
thecorrespondingcurrentlevels,whereastheIEEEstandarddoesnot.Reference[6]gave
the typical range of these currents for station airbreak equipment
from72.5kV to 1200kV. This is the newest IEC technical report,
released in 2009,whichdescribes thecapacitivecurrentswitchingduty
forhighvoltageairbreakDSsforratedvoltagesabove52kVandprovidesguidanceonlaboratorytestingtodemonstrate
the switching capability. This is also the first time to provide
ananalysisoftheswitchingdutyandtodefinetestingprocedures.1.5ObjectiveofthesisAmong
these three main applications of current interruption using DSs,
loopcurrent interruption has been investigated in detail in [4]. As
compared
toinductivecurrent(excitationcurrent)andresistivecurrentswitching,acapacitivecurrent
is a more challenging to interrupt because of the trapped
chargeremainingontheloadtobeswitched(Chapters3,5).IntheIEEEstandard[8],theessentialdifferencebetweencapacitivecurrentandexcitationcurrent
ispointedoutas:"This type of capacitive interruption is similar to
excitation current interruption inwhichthere is a succession of
interruptions near zero current, each followed by restrikes.
Thedifference between the two types of interruptions is that for
each capacitive currentinterruption,a charge ismore likely tobe
retainedby the capacitivedevice.Eachof
thesetrappedchargescreatesanadditivebiasvoltagethatincreasestheprobabilityofrestrikingacross
the open gap of the switch 1/2cycle laterwhen the source voltage
has reversed itspolarity.Consequently,
longerarcreacheshavebeenexperiencedwhenswitchingcapacitivecurrentsthanwhenswitchingexcitationcurrents."CertainlycomparedwithswitchingonthecapacitivecurrentwithDSs,switchingoff(interrupting)capacitivecurrentisamoreseveretask.
-
6Chapter1
Itwasmentioned that a socalled "negligible current" doesnot
exceed0.5A
forratedvoltagesof420kVandbelow.Inthepast,thecurrentinterruptingcapabilityof
airbreakDSs therefore has been taken as 0.5A or less. However, at
presentwith the fast development of power networks, users
requirement for smallcapacitive current interruption using airbreak
DSs is frequently higher due tocomplexity of the network or
financial reasons. The subject of this
thesis"InterruptionofcapacitivecurrentbyHVairbreakdisconnectors"addressesthechallengingtaskofinterruptingrelativelylargecapacitivecurrents(uptofewtensofamperes).CapacitivecurrentinterruptionwithaDSconsistsmicroscopicallyofasuccessionof
interactiveeventsbetweenthepowercircuitandtheACarcwitharepetitivesequence
of interruptions, reignitions/restrikes. The arc reestablishment
ischaracterized in terms of oscillations and transients of current
and voltage,recovery voltage. The interruption process is
characterized in terms of arcduration, arc reach (perpendicular
distance of outermost arc position to a lineconnecting the
contacts), arc type (repetitive or continuous), arc
brightness,energyinputintothearc,andsoforth.Thisdissertationwillparticularlyfocuson:
TheprinciplemechanismofthecapacitivecurrentinterruptionusingHVair
breakDSs.It
includesthetransientvoltageandcurrent,energyinputofthecircuit,restrikevoltage,etc.
Thephenomenaoftheswitchingarc,includingdifferentfeatures,suchasarc
voltage,arccurrentandotherphysicalcharacteristicssuchasarcbrightness,arc
length,arcduration,arcreach,archeight,basedontheanalysisofdatafromopticalandelectricalexperiments.
Influencing factors on the transient and arc phenomena,which
include the
ratioofthesourceandloadsidecapacitances,powersupplyvoltage,currentleveltobeinterruptedandrestrikevoltagefromtheelectricalside.Fromthephysical
side, the influencesof (forced)arc coolingand
(forced)elongationareanalyzedexperimentally.
Thebreakdownvoltageandtheprebreakdownmechanismintheairduring
thenumerousreignitionsandrestrikes.
Approachestoenhancetheinterruptioncapability.
i. Anairflowsystemassistingarcquenchingii.
Auxiliaryhighvelocitycontactsiii.
Insertionofresistorsintothecircuitiv.
Otherapproaches(discussiononly)
-
HighVoltageAirbreakDisconnectors7
The research is carried out based on experiments in different
laboratories.Development and preliminary experiments are done at
the high
voltagelaboratoryofEindhovenUniversityofTechnology.FullscaletestsareperformedatKEMAHighPowerLaboratoriesinArnhemandPrague.ThetestobjectDSsaresuppliedbyHAPAMB.V.,theNetherlands.References[1]
IEVnumber4411405,[online].
Available:http://std.iec.ch/iev/iev.nsf/display?openform&ievref=4411405.[2]
IEEE StandardDefinitions for Power Switchgear, IEEE Standard
C37.1001992, Oct.
1992.[3]
J.D.McDonald,ElectricPowerSubstationsEngineering,London:CRCpress,2007.[4]
D. F. Peelo, "Current interruption using high voltage airbreak
disconnectors", Ph.D.
dissertation,Dept.ElectricalEngineering,EindhovenUniv.ofTechnology,Eindhoven,2004.
[5] IEEE Guide to Current Interruptionwith HornGap Air Switches,
American
NationalStandard(ANSI)IEEEStandardC37.36b1990,Jul.1990.
[6] IECTechnicalReport IEC/TR62271305, "Highvoltage switchgear
and controlgearPart 305: Capacitive current switching capability of
airinsulated disconnectors forratedvoltagesabove52kV",Nov.2009.
[7] IEC Standard on "High voltage switchgear and control
gearPart 102:
Alternatingcurrentdisconnectorsandearthingswitches",IEC62271102,Dec.2001.
[8] IEEEStandardDefinitionsandRequirements forHighVoltageair
switches, insulators,andbussupports, American National Standard
(ANSI) IEEE Standard C37.3Oh1978,Jun.1978.
[9]
AmericanNationalStandardDefinitionsandRequirementsforHighvoltageAirSwitches,Insulators,
and Bus Supports, American National Standard (ANSI) IEEE
StandardC37.301971,Apr.1971.
-
8Chapter1
-
LiteratureReview9
Chapter2
LiteratureReviewFromthehugenumberofpublicationsondevicesappliedinpowersystems,thereappearstoexistonlyalimitedamountofpapersonairbreakDSs.Especially,onlyafewofthemareactuallyconcernedwiththephenomenarelatedtofairlysmallcapacitive
current interruption with DSs in high voltage systems. The
reviewpresented in this chapter is based on selected papers
(partly) related
tointerruptionofsmallcapacitivecurrent.Inparticularthischapterwillinvolvefivetopics:
EngineeringguidelinesoncurrentinterruptionwithairbreakDSs.
Fundamental aspects of capacitive current interruptionwith a
standalone
DS(i.e.withoutanyauxiliarydevicestoaidinterruption).
TransientscausedbyDSswitching.
ApproachestoimprovecapacitivecurrentinterruptingcapabilityoftheDS.
Possiblearcmodelsrelatedtothecurrenttopic.2.1AwarenessofthecapacitivecurrentinterruptionwithdisconnectorsF.
E. Andrews et al. belonged to the earliest authors on the field of
currentinterruptionwith airbreakDSs. They carriedoutnumerous
laboratory tests ontransformer excitation current, loop current
switching at 33kV level and linedropping at 132kV using DSswith
horngap on the Public Service Company
ofNorthernIllinois,USA,inthe1940s.Theresultswerepublishedinathesis[1]andinasubsequentpaper
[2].A typicalhorngapdevice (alsocalledarcinghorn)
isshowninFigure2.1.Thehorngapnormallyactsasthelastpointofmetaltometalcontact
on the DS when opening. Thus the arc burns between the arcing
hornratherthanbetweenthemainbladesoftheDS.Thegoalofthesetestswastofindthe
correlation between the voltage across the DS after switching off
and
theinterruptedcurrentononehand,andthearclength,reachontheotherhand.Thearclengthwasdefinedasthecompletelengthoftheirregularpathfollowedbythearc.Thearcreachwasdefinedasthedistancefromapointmidwaybetweenthebladeendstothemostremotepointofthearcatthetimeofitsmaximumlength(seeFigure2.2).
Itwasrecognizedthatthearc
lengthscaledproportionaltothearcvoltage.Themainattentionwaspaidto"arcreach",sinceitwasconsideredtobemoresignificantthanthe"arclength"inswitchingoperationsifthephasetophaseandphasetogroundclearancewereconsidered[2].Forthisreasonthearcreachhasbeentakenasameasuretoprovideacriterionforswitchingclearance.
-
10Chapter2
Figure2.1.ArcinghornmountedonaverticalbreakDS(copiedfrom[50]).
Figure2.2.DefinitionofarcreachandlengthaccordingtoAndrewsetal.[2].TheoverallresultsplottedinFigure2.3,copiedfrom[2],presentthearcreachintermsof
"feetperkilovolt"asa functionof initial
interruptedcurrent.Fromtheresults,thecriticallimitsdescribedthe"LimitoftheProbableReach"(LPR)ofthearc,werederivedforexcitationcurrentandloopcurrentinterruption:
LPR=5.03UocI,when0Cl.ThemaximumcurrentthroughtheDSintheHF loop
is H Hr C LU (neglecting HF damping). Obviously, iH increases
withincreasingUrandCHanddecreaseswithincreasingLH.ThusUrandCs/Cl(orCl/Cs)arekeyparameters
that affect theHF transientbehaviouron
restrikes.TheHFtransientsinthecurrentarecandidatestocauseelectromagneticinterferenceinsecondarysystems,as
itwillbereported inChapter5.Giventhehighfrequencyand amplitude
derivatives of the current, up to a few kiloamperes
permicrosecondsinlatertests,itcancoupleinductivelywithneighbouringcircuitry.Also,itprovidesasignificantpowerinputintotherestrikingarc,albeitduringalimitedtime.3.2.2Mediumfrequency(MF)componentUpon
restrike, also a "mediumfrequency" (MF) oscillation starts. The
MFcomponent,whichlastsaboutafewmilliseconds,alsocausesatransientvoltageandcurrent.AtthisstagethevoltageacrossthearcisneglectedandtheanalysisstartsafterdecayoftheHFtransient,withvoltageofeachcapacitorequalizedtoUE.LHinFigure3.3isneglectedaswell,becauseitsequivalentimpedanceismuchsmaller
than the capacitances impedance at MF. Therefore, Cs and Cl with
anidenticalinitialvoltageUEareinparallelandtheequivalentcircuitofFigure3.1atMF
applies. Because of the charge redistribution during the HF
oscillation,
thevoltagesacrossCsandClhavechanged,andwilldischargeviaLsandRsduringthedurationoftheMFoscillation.The
instant of restrike is again taken as t = 0. On the time scale of
the MFoscillation, us can be treated as a constant (Em sin).
Similarly as for the
HFanalysis,uCM(thevoltageacrossCsandCl),andiM(thecurrentthroughtheDS)canbedetermined:
-
40Chapter3
0
2
sin e sin( )11 e sin( )(1 )
M
M
tMrCM m M M
s l M
trM M
s Ms l
Uu E t
C CU
i tLC C
(3.4)
where 2 2 20 01 , , , arctan2 ( )
S MM M M M M M
S S s l M
RL L C C
.TheoscillationfrequencyMmainlydependsonthesumofbothcapacitancesandthe
inductance Ls. In general the frequency of this oscillation is in
the order
ofseveralkilohertz.Similarlyasforthehighfrequencytransient,thevoltagesduringtheMFoscillation
across both capacitanceswith initial voltagesUE are dampeddue to
the equivalent resistance in the loop and finally reach the value
us. Themaximumvoltageacrossthecapacitancesis sin 1
rm
s l
UEC C
.Itincreaseswithincreasing Ur, ratio Cl/Cs and Em Similar to the
HF oscillation, the maximumtheoretical voltage is 3Em. The maximal
current during the MF oscillation is:max(iM) 21 (1 )
r
s l s M
UC C L ,whichdependsonUr,Cs/ClandLsaswell,andscales
withUr.3.2.3ThreecomponentssynthesisAfterHFandMFcomponentshavedampedout,onlythePFcomponentremains.Sincethetimeconstantsinvolvedarehighlydistinct,theHFcomponentvanishesonthetimescalefortheMFoscillationandtheMFoscillationhasdisappearedonthe
timescale forPF.The initialvoltage,atwhichtheMFoscillationstarts,
is
thefinalsteadystatevoltageafterHFoscillationdecayandtheinitialvoltageforthePFoscillationisthefinalsteadystatevoltageoftheMFoscillation.Inordertoquantifythecompletetransientbehaviour,thethreecomponentsarecombined.
The voltage ucl across the load side capacitance and the current
idflowingthroughtheDSonrestrikecanbewrittenas:
0 0
2
e sin( ) e sin( ) sin( )1 11 e sin( ) e sin( ) cos( )(1 )
H M
H M
t tH Mr rcl H H M M m P
l s H s l M
t tr rd H M l P m P
H H s l s M
U Uu t t E tC C C C
U Ui t t C E tL C C L
(3.5)
-
BasicCircuitAnalysis41
Figure3.4. Simulatedwaveshapesofucs,ucl,udduringonepower
frequencycycleuponrestrike.Equation(3.5)containsthethreefrequencycomponentsinthevoltageacrosstheloadsidecapacitanceandinthecurrentthroughtheDSarc.Thevoltageacrossthesourcesidecapacitancecanbecalculatedinasimilarmanner.Itturnsoutthatthetransientvoltagesandcurrentsdependontheairgapbreakdownvoltage,voltagesupply
level, the ratioofCs/Cl andso forth In the following sections
thedistinctfrequency contributions to overvoltages and currents
will be discussed on
thebasisoftheanalysisaboveandcomparedwithexperimentaldata.3.3SimulationofrestrikesFor
illustrating the restrike phenomena in voltage and current
waveforms asimulation is performed using MATLAB Simulink
(SimPowerSystems). Theparameters taken are: Em=702kV, Ls=10mH,
Cs=10nF, Cl=100nF,
theresistanceforarcatrestrikeistakenas20andLH=15H.Initially,theDSisinclosed
position. The DS gap starts to recover at t=5ms, and restrikes
att=10ms. The simulated wave shapes for the current id, voltages
ucl, ucsand udtogether with their zoomed in of the HF and MF
components, are plotted inFigures 3.43.6. In Figure 3.4, the
threecomponents are indicatedwith arrows.According to Section3.2,
the charges of the source and load side
capacitanceCsandClexchangeduringthehighfrequencyperioduntiltheequalizationvoltageUEis
reached, shown in Figure 3.5. The mediumfrequency component, after
thehighfrequencyoscillationhasdisappeared,
isdepictedinFigure3.6.Inasimilarway, the wave shapes of the current
id and its high and
mediumfrequencycomponentsareshowninFigures3.73.9.It can be observed
that the high andmediumfrequency components last
about10sand23msrespectivelyinthissimulation.Duringtheoscillation,thereisatransient
currentwith a peak value up to 2kA upon restrike at t=10ms.
TheobservedovervoltageacrossthesourcesidecapacitanceCsis1.5p.u.
0 5 10 15 20200
100
0
100
200
time (ms)
Vol
tage
(kV)
ucl ucs ud
MF
PF
HF
-
42Chapter3
0 5 10 15 204
2
0
2
time (ms)
Curre
nt (k
A)
10 10.01 10.02 10.03 10.04 10.05 10.062
1
0
1
time (ms)
Curre
nt (k
A)
Figure 3.5. Simulated wave shapes of ucs, ucl, ud at
highfrequency (zoomed in
fromapproximately9.96msto10.06msinFigure3.4).
Figure 3.6. Simulated wave shapes of ucs, ucl, ud at
mediumfrequency (zoomed in
fromapproximately9.5msto12.5msinFigure3.4).Figure3.7.Simulatedwaveshapesofidoveronepowerfrequencycycleuponrestrike.
Figure3.8. Simulatedwave shapesof idathighfrequency (zoomed in
fromapproximately10.00msto10.06msinFigure3.7).
0 5 10 15 20 25100
0
100
time (s)
Vol
tage
(kV)
ucl ucs ud
UE
9.5 10 10.5 11 11.5 12 12.5
100
0
100
time (ms)
Vol
tage
(kV)
ucl
ucs
ud
-
BasicCircuitAnalysis43
Figure3.9.Simulatedwaveshapesofidatmediumfrequency(zoomedinfromapproximately9.5msto12.0msinFigure3.7).3.4RestriketransientsindistributedelementloadcircuitsInthecircuitofFigure3.1onlylumpedcomponentsareconsidered.Asmentionedin
Chapter 1, the capacitive current to be interrupted arises from
substationcomponents,suchascurrenttransformer,capacitivevoltagetransformer,butalsofromdistributedelements,suchasbusbars,overheadline,andpowercables.If
thephysicaldimensionsof theconsideredcomponentsaremuchshorter
thanthewavelengthcorrespondingwith
thecurrentandvoltageoscillations, lumpedparameters can be used to
model the power system. Otherwise, a distributedparameter approach
has to be adopted. The transmission line specific (per
unitlength)parametersL,C andR (G isomittedsince theair
isconsideredaperfectinsulator) are uniformly distributed over the
length of the line. For the
steadystateoperation(powerfrequency,50Hzor60Hz),thetransmissionlinescanberepresentedby
lumpedparameters.But for transientbehaviour the lines
itmaybenecessarytoberepresentedbydistributedparameters.During the
capacitive current interruption by a DS, transient phenomena
occurwithhighfrequencycontent,duetotherepeatedbreaksandrestrikes.Therefore,a
distributed parameter simulation for transmission lines is
considered in
thissection.Thesimulatedresultsofalumpedparameterandadistributedparameterapproachofatransmissionlinearecompared.ThevalueofthelumpedelementparametersinFigure3.10aretakentoproducethesamepowerfrequencyresultsasthoseinFigure3.1.Theunloadedoverheadline
is simulatedwithdistributedparameters.A line lengthof50km is taken
tomatch the interrupted current Id (PF current of 9A) of the lumped
circuit
(linecapacitanceandinductanceare8.48nF/kmand1.33mH/km,matchingalumpedload
side capacitance ofCl = 424nF). The simulated results are shown in
theFigures 3.113.13,where thewave shapes of the interrupted current
id and
thevoltageacrosstheDSud,arepresentedrespectively:id1,ud1aresimulatedresultsfromsimulationwithdistributedelements,
and id2,ud2 are simulated results
areobtainedfromsimulationwithlumpedelements.
9.5 10 10.5 11 11.5 12
0.20.1
00.10.2
time (ms)
Curre
nt (k
A)
-
44Chapter3
20 21 22 23 24 2564
2
02
4
time (ms)
Vol
tage
(kV)
ud2
ud1
Figure3.10. Simulated circuit for capacitive current
interruptionwitha transmission
linerepresentedbydistributedparameters.
Figure3.11.(Left)waveshapesofthecurrentid1,id2throughtheDSwithdistributedlinesandlumpedcapacitancerespectivelyand(right)expansionofid1between22.4msand23.2ms.
Figure 3.12. Wave shapes of the voltage ud1, ud2 across
theDSwith distributed lines andlumpedcapacitancerespectively.
The wave shapes of current and voltage show that the travelling
waves arereflected within 0.33ms. There are transient phenomena on
each
reflectionmoment(seeFigure3.11,3.12).Nevertheless,thereishardlyanyhighfrequencycomponent
at restrikes in the voltage and current waveforms with
thedistributedparameters,which consequently reduces the total
amountof energy
15 20 25 30
200
0
200
400
time (ms)
Curre
nt (A
)
id2 id1
22.4 22.6 22.8 23 23.2
100
0
100
time (ms)
Curre
nt (A
)
-
BasicCircuitAnalysis45
inputintothecircuituponrestrike.Thisisbecausethehighsurgeimpedanceofthe
line (in thisexample390) limits theHFrestrikecurrentcompared to
themuch lower surge impedanceof the lumped capacitor.Therefore, to
interrupt acircuit with lumped parameters is a more severe task as
compared to
aconfigurationwithdistributedparameters.Intheanalysisinthischapter,andalsointheexperimentalarrangementdescribedinthefollowingchapters,circuitswithlumpedelementsareapplied.Thispointshouldbepaidattentionto,becauseofitsimpactontesting,wherenormally(lumped)capacitorbanksareused.3.5ConclusionThemainobservationswithrespecttocalculationsandsimulationsoncapacitivecurrentinterruptionwithhighvoltageairbreakDSsare:CapacitivecurrentinterruptionbyaDSconsistsofrepeatedbreaksandrestrikesasaconsequenceoftheinteractionbetweenarcandcircuit.The
transient upon restrike consist of threecomponents: high, medium
andpowerfrequencycomponent.Duringthehighfrequencycomponent,thetransientperiod
is in the order of a few tens of microseconds. The
mediumfrequencycomponent is in the order of a few milliseconds. The
overvoltage across
thecapacitancesatbothsidesoftheDScanbeupto3p.u.theoretically.Thepeakofthetransientcurrentmaybeuptoafewkiloampereswithinafewmicroseconds.Theratioofsourceandloadsidecapacitance,therestrikevoltageandthecurrentto
be interrupted are the key factors that influence the transient
voltage
andcurrentmagnitudesuponrestrike.Thecircuitwithlumpedelements,whichisadoptedinthisthesis,isaworstcaseapproach.
Capacitive current interruption of transmission lines where
adistributedparameterapproachappliesislesssevere.References[1]
IECTechnicalReport IEC/TR62271305, "Highvoltage switchgear and
controlgear
Part 305: Capacitive current switching capability of
airinsulated DSs for ratedvoltagesabove52kV",Nov.2009.
[2]
L.vanderSluis,"TransientsinPowerSystems",Chichester:JohnWiley&Sons,2001.[3]
D.F.Peelo,"CurrentinterruptionusinghighvoltageairbreakDSs",Ph.D.dissertation,
Dept.ElectricalEngineering,EindhovenUniv.ofTechnology,Eindhoven,2004.
-
46Chapter3
-
ExperimentalSetup47
Chapter4
ExperimentalSetupExperimentsinthisthesisareperformedatseverallocationsemployingdifferenttypesofvoltagesources.ThebasiccircuitdiagramforalltestsiteswaspresentedinFigure3.1.Figure4.1depictsthegeneralsetupincludingthemeasuringsystemschematically.The
voltage supply is represented by an ideal voltage source us with
seriesresistanceRs representing losses and inductanceLs. Their
valuesdependon thesource type being used (see Section 4.1).
Capacitances Cs and Cl stand for
thesourceandloadsidecapacitorbankswithaDSinbetween.Thecapacitancevaluescanbevariedforthetestseries.Thevoltagesucs,uclarethevoltagesacrossCsandCl,respectively.ThesevoltagesaremeasuredbythecapacitivevoltagedividersD1andD2incombinationwiththehighvoltageprobesD3andD4(Section4.2.1).Thedifferentialsignal
isusedtodetermine thevoltageacross theDS(Section4.2.2).Thecurrent
throughtheDS is indicatedby id.Current transformersCT1andCT2measure
the current through Cl (Section 4.2.3). Two current transformers
areapplied to cover the dynamic range of different frequency
componentssimultaneously (below 1A to several kiloamperes and from
50Hz to
severalmegahertz),denotedasipfandihf,respectively.Voltagesandcurrentsarerecordedbyadataacquisitionsystemincludingfourdigitizers,CH14,eachhavingasingleinputchannel(Section4.2.4).
Inadditionto theelectricalsignals,arc
imagesarerecordedbymeansofahighspeedcamera,whichisinstalledonthesameheightas
the DS blades (Section 4.2.5). The opening characteristics of the
DS isdeterminedinSection4.3.4.1HighvoltagesourceTwodifferent
typesofhighvoltagesourceareemployed.Dependingon the
testsites,apowertransformeroraresonancehighvoltagesourceisused.A
shortcircuit generator plus a transformer are available in large
scalelaboratories,suchasKEMAHighPowerLaboratoriesinArnhemandPrague.TheequivalenttestcircuitisshowninFigure4.2.AsourceinductanceLsisusedwithavalue
up to a few hundreds of millihenry. Air gaps are used to protect
thecapacitors bank, but are not shown in Figure 4.2. These setups
supply up to173kVrms phasetoground voltage, and up to 27A current
during theexperiments. The specific test configurations employed
for different series
ofexperimentswillbepresentedinChapters5,6and7.
-
48Chapter4
Figure4.1.Experimentalcircuitincludingelectricalandopticaltransducers.
Figure 4.2. Test circuitwith source in KEMA HPL. G: shortcircuit
generator;M:masterbreaker; Ls, Rs: reactor and resistor at source
side; S: make switch; TR: shortcircuittransformer.In the high
voltage laboratory at the Eindhoven University of Technology
aresonantsystem(Hipotronics)isavailableashighvoltagesupply.ItstopviewandequivalentschemeareshownFigure4.3(leftandright,respectively).TheresonantsystemincludesanadjustablehighvoltagereactorLs,acapacitorCand
an exciter transformer. The variable auto transformer T1 controls
thetransformerT2,whichsuppliespower to the resonant circuit, and it
isolates
thetestspecimenfromtheline.Twotuneablereactors,whichcanbeconnectedeitherin
series or in parallel, make up the source inductance. Each of them
has
aninductancewithavalueintherangeof400H10kH,andresistance(measuredatDC)
of about 1k. Each reactor is designed for a voltage of 300kVrms.
TheAC
-
ExperimentalSetup49
Figure4.3. (left)Laboratory source forcapacitivecurrent
interruptionwithaDSatTU/e;(right)simplifiedschematicsofHipotronicshighvoltagesource.sourcepoweringtheresonantcircuit,indicatedwithuoutinFigure4.3(right)isatmaximum
22kVrms. The capacitanceCs is chosen either 2nF or 4nF by
seriesconnectionsoffourortwo8nF,150kVcapacitors.Differentcombinationsoftenavailable
16nF high voltage capacitors can be made to adjust the
(load)capacitanceCltothedesiredcurrent.Eachofthesecapacitorshasaratedvoltageof150kVrmsandtan